Men who have sex with men (MSM) continue to represent the largest risk group in the on-going HIV epidemic in the United States and African American MSM are disproportionately affected by HIV. Substance- abusing sexual minorities warrant increased attention as they are more likely to be untreated or under-utilize treatment, at elevated risk for HIV and a potential HIV bridge population to non-drug using populations. A gap in the MSM substance use literature is consideration of the heterogeneity of alcohol and drug use patterns. Identifying and defining these patterns can improve specification of risk groups and more efficient allocation of treatment and prevention resources. Latent class analysis (LCA) is a well-accepted inductive statistical method that provides data derived classifications of patterns of alcohol and drug use. The proposed study will use LCA to empirically define and characterize drug and alcohol use patterns of an existing dataset of n=368 African American men who have sex with men (AA MSM) and to examine differences in HIV risk by pattern of use. LCA also can improve understanding of the social and environmental context to substance use and HIV risk. Less is known about how network dynamics vary by patterns of drug and alcohol use. Two understudied, but critical features of social networks that directly pertain to disease transmission dynamics are multiplexity (e.g. overlap in sexual and drug use networks) and density of sex and drug networks. In the proposed study we will examine associations between substance use patterns of AA MSM and network dynamics to expand understanding of the intersection between drug use and HIV risk. Finally, the proposed study will examine the spatial distribution of MSM by pattern of their alcohol and drug use to examine how neighborhood context influences the intersection between substance use and HIV risk. This research is informed by the risk environment framework and findings will provide an empirical foundation for developing tailored HIV and substance use prevention interventions. Furthermore, this study will contribute to advancing the goals of the National HIV/AIDS Strategy,39 by focusing on communities with heavy concentration of HIV/AIDS, particularly MSM, African Americans and substance abusers.